This invention relates to a draw bar construction for collet chucking spindles, such spindles being those usually used in machine tools and in this particular instance especially arranged for use in conjunction with what is known as a Bridgeport milling machine, which is a well known vertical type machine tool of very versatile application.
A machine tool of this nature, includes a spindle, hollow and which is designed to be driven at various varying speeds by suitable motor, the entire unit mounted in what may be termed a vertical fashion on a column and with a suitable table upon which the workpieces may be supported.
The spindle of the machine is in turn arranged to have supported on its lower end a collet in most uses in which is intended to be engaged a tool for operation on part supported on the table.
It is thus necessary to have the collet operated and to this end the spindle is hollow and a draw bar of known configuration is arranged to be received within the spindle and in turn engage the collet to draw the same inwardly and outwardly and thus grip the tool for rotation and application to the workpiece supported in position therefore.
The foregoing is generally conventional and specifically the drawbar currently availed of includes a wrench head at one end, having normally the usual six sided or hexagonal flat faces of elongated nature, with a face adapted at its lower end to engage the spindle and draw up the bar, which in turn is provided at its lower extremity with threads for contact with the collet which is carried in the spindle and in turn grips the tool for operation thereof.
Wear takes place on the threaded portion of these drawbars and eventually is sufficient to require that they be replaced if other means for extending the lift are not provided.
In this particular invention, there is disclosed and availed of an arrangement of drawbar which involves the use of an elongated body of conventional form having a wrench head at one end and the threaded area at the opposite, but in this instance the threaded area is of elongated nature and separated by a notch or V section, at which point the extreme end thread or first section thread could be removed when worn thus bringing into position the second section thread for operation and engagement with the collet.
However since this will necessarily shorten the length of the drawbar body, a suitable spacer is necessary to provide and that is arranged so as to be removed from the body and thus again make the relationship between the wrench head and the threads such as to be able to operate the collet.